Electric contact



c. F. CARPENTER 1,770,839

ELECTRIC CONTACT July 15, 1930'.

Fiied NW. 1. 1926 coated with cadmium Inv entb Patented July 15 1 30, n 1,770,839

,UNITED' STATES pATENT- ICE cmmrns 1+. canrmrran', or SCHENECTADY, NEW Yonx, assrcnoa 'ro GENERAL.

mnc'rarc commune-a conrona'rron or NEW Yonx amscrmo con'racr Applicationflled November 1, 1926. Serial No. 145,442.

This invention relates to electric contacts, of fuses, switches, or the'like,'may be limited and itisparticularly concerned with the con- I so that overheating does not result even durtact resistance inherently existing at the ing long continued service under conditions junctions of conductors that'are included in which would normally cause oxidization and 6 anelectric circuit. Thus, when two condeterioration of the contacts. '55

ductors of copperor other metal are mechani- This is accomplished in accordance with cally held in contact to permit electriccurthe present invention by providing the conrent to flow therebetween, there is a restricductors with a contact surface of cadmium. ti ve resistance to the current flow at the joint. I have found that copper contacts provided 10 This is due primaril to the fact that the with a coating or facin of cadmium at the 60 actual contact is ma e only at oneor more contact surfaces are capa 1c of long continued small points and the current is therefore service without developing any appreciable forced to flow across these small restricted restrictive resistance at the contacts and, connections. therefore, without any increased heating ef- Since the contact resistance between most feet at the contacts over long periods of serv- 05 all metallic conductors is increased as the con-' ice while carrying full load current through tact surface of the conductor becomes oxid the contacts. ized, undesirable localized heating is likely to Fig. l of the accompanying drawing shows develop at the contact between the conducan ordinary type of fuse mounted in fuse tors, particularly with the conductors in circli s with both the end ferrules of the fuse 70 cuits carrying currents of an appreciable an the fuse'clips provided with a coating of magnitude. This is particular ytrueof copcadmium, as illustrating one way in which per conductors, as'the copper oxide is a very the invention may be carried into effect. poor conductor. Since copper is the metal F ig.2shows the main current carrying conprincipally used for the current carrying tact ofadouble break circuit interrupter pro- 75 parts of electrical devices for the reason that vided with a facing plate of cadmium in acit hasthe lowest ohmic resistance of any of cordance with the invention. S the cheap metals, considerable difficulty due 'In Fig. 1 the fuse 10 is of the usual type to the localized heating at the contacts of copprovided with the copper or brass Tend ferper conductors has been experienced in most rules 11 and 12 which are arranged to be reso all types of electrical a paratus. Thus, for ceived-in the copper or-brass fuse clips 13 example, when an or 'nary type of fuse and 14 mounted upon the base 15. The fermounted in fuse clips is included in an elecrules 11 and 12, as'well as the fuse clips. 13 tric' circuit,- the contact resistance between and 14, are then provided with a substantial the copper end ferrules and the copper fuse coating of cadmium, preferably by electro- 85 clips may roduce a heating effect which malytic deposition of the cadmium thereupon. terially affects the normal rating of the fuse, As there are various well-known methods particularly -after the fuse has been in service of roducing a satisfactory electrolytic desufliciently long for the contact surfaces of the position of the cadmium upon a foundation 40 end ferrules and the fuse clips to become thormetal such as copper, brass, or other low re 00 oughly oxidized. Likewise, with. an ordi-. sistance conducting material, it will be undernary switch having contacts of copper that stood that the particular method employed is have become oxidized, such localized heating not of the essence of the present invention, at thecontacts may develop that the switch and hence no further description thereof is is incapable of satisfactorily. carrying the deemed necessary.

normal load current for which it' was de- I have found that the cadmium coating, signed. such as described above, is particularly ad- My' present invention provides improve- -vantageous in reducing the contact resistance ments whereby the contact resistance of elecwhere the electric conductors are held in contric conductors, particularly at the cl mtacts tact with only a light pressure, and are not y 2 p i 1,770,889

- subjected to any appreciable wear, as in the I tively movable contacts ving cooperating contact surfaces of cadmium for preventing I contacts.

the main current carrying contact 16 of-thc circuit interrupter is provided with a relatively thin facing plate 17 formed of cadmium. Likewise, the stationary contact 18 also may be provided with a thin facing plate '19 of cadmium. The cadmium facing plates 17 and 19 may be secured to the respective contacts 16 and 18 in any suitable manner, although preferably the facing plates are sweated or soldered to the contact member.

As the are occurring upon the opening of the circuit interrupter shown in Fig. 2 is restricted entirely to the auxiliaryarcing contacts 20 and 21 which are maintained closed until after the separation of the main currentcarrying contacts 16 and 18 in the'usual'manner," the cadmium facings of the main current-carryin contacts are not subjected to the pitting,- urning, or other destructive'ac-( tion of the arcs. Dueto the-fact that the contact resistance between the cadmium facings 17 and 19 remains at a substantiallv con stant value throughout along period of service, there is no tendency for the main current-1 carryin contacts 16 and 18 to become overheated ue to localized heating at the junction' therebetween. Consequently, the interrupter provided with contacts embodying the present invention is capable of continuedservice i at full load curent over long periods.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1.' An electrical contact formed of .opper and provided with a coating or facin of cadmium on the contact surface thereof or maintaining the contact resistance of the contact substantially constant.

2. An electrical contact havingza cadmium contact surface for preventing increase in the contact resistance of the contact.

3. An electrical device rovided with relaincrease in the contact resistance between the 4. A fuse having a coating ofcadmium electrically deposited onits contacts.

5. In combination, a pair of electrical conducting members having cooperating contact surfaces thereon, each of said members comprising a low resistance foundation nietal with a contacting surface of cadmium.

In witness whereof, I have hereunto set my hand this 29th da of Octotber, 1926. r

a C S Fl CARPENTER 

